Technical Field
This technology relates to stab resistant, closed woven composite articles formed by thermally fusing an open woven fabric formed from high tenacity, thermoplastic elongate bodies, and to a continuous process for forming the composite articles.
Description of the Related Art
High tenacity fibers, such as SPECTRA® polyethylene fibers or aramid fibers such as KEVLAR® and TWARON® fibers, are known to be useful for the formation of articles having excellent ballistic resistance. Ballistic resistant articles formed from high tenacity tapes are also known. Articles such as bullet resistant vests, helmets, vehicle panels and structural members of military equipment are typically made from fabrics comprising high tenacity fibers or tapes because of their very high strength to weight performance. For many applications, the fibers or tapes may be formed into woven or knitted fabrics. For other applications, the fibers or tapes may be encapsulated or embedded in a polymeric matrix material and formed into non-woven fabrics. In one common non-woven fabric structure, a plurality of unidirectionally oriented fibers are arranged in a generally coplanar, coextensive relationship and coated with a binding matrix resin to bind the fibers together. Typically, multiple plies of such unidirectionally oriented fibers are merged into a multi-ply composite. See, for example, U.S. Pat. Nos. 4,403,012; 4,457,985; 4,613,535; 4,623,574; 4,650,710; 4,737,402; 4,748,064; 5,552,208; 5,587,230; 6,642,159; 6,841,492; and 6,846,758, all of which are incorporated herein by reference to the extent consistent herewith.
Composites fabricated from non-woven fabrics are known to stop projectiles better than woven fabric composites because the component fibers in non-woven fabrics are not crimped like the fibers in woven materials. Fiber crimping reduces the ability of the fibers to stay in tension and immediately absorb the energy of a projectile, compromising their effectiveness. In addition, projectile damage to non-woven fabrics is more localized compared to woven fabrics, allowing for enhanced multi-hit performance. However, woven composites are more stab resistant than traditional non-woven fabrics formed from parallel fiber arrays, because the mechanically interlocking woven fabric structure creates superior friction than that is better at preventing blades from piercing through the fabric.
Nevertheless, stab resistant woven fabric articles of the related art remain imperfect. Such woven fabrics require a very tight weave (i.e. a pick count of greater than 56×56 per inch) so that the fabric or fabric layers will not shift on blade impact and to create sufficient friction to prevent the blade from piercing the fabric. Creating woven fabrics of such high density requires the use of very fine, high quality yarns that are expensive to manufacture. Also, the use of such fine yarns requires that they be highly twisted and/or highly commingled, but the fine yarns are delicate and often break during twisting or commingling, keeping productivity low. Finally, composites formed from twisted fibers are less effective at stopping bullets or other projectiles than composites formed from untwisted fibers. Accordingly, there is an ongoing need in the art for improved woven ballistic resistant composites having both superior stab resistance and superior ballistic resistance. The present invention provides a solution to this need.